1. Field of the Invention
The present invention relates to an image forming apparatus and method, wherein a color image or a monochromatic image is formed on an intermediate transfer medium and then, the image on the intermediate transfer medium is secondarily transferred to a recording medium such as a copy sheet, transfer sheet, paper sheet, or transparent sheet for OHP. In this apparatus, the color image is formed by superimposing a plurality of toner images in different colors on top of each other on the intermediate transfer medium such as a transfer belt, a transfer drum or a transfer sheet. Further, the monochromatic image is formed by transferring a monochromatic toner image to the intermediate transfer medium.
2. Description of the Related Art
In the image forming apparatus of this type, an electrostatic latent image is formed by irradiating a light beam on a latent image carrier such as a photosensitive member and a toner image is formed by developing the electrostatic latent image with toner. The toner image thus formed is primarily transferred to the intermediate transfer medium. Subsequently, the toner image is secondarily transferred to the recording medium at a suitable timing. In order to carry out the secondary transfer, a secondary transfer device, such as a secondary transfer roller, is provided being free to abut on or to be cleared from the intermediate transfer medium. And a timing on when the secondary transfer device abuts on the intermediate transfer medium is properly controlled (see, for example, Japanese Unexamined Patent Publication No. 2001-92267).
According to the apparatus disclosed in this Japanese Unexamined Patent Publication No. 2001-92267, a charging process by a charger roller is started at a proper timing and is followed by an exposure process, whereby the electrostatic latent image is formed on the photosensitive member. The electrostatic latent image is developed by a developing device containing a yellow toner, thereby forming a yellow toner image, which is primarily transferred to the intermediate transfer medium. Such an image forming process (exposure process—development process—primary transfer process) is repeatedly performed in the order of yellow, magenta, cyan and black, whereby a color image is formed on the intermediate transfer medium. The color image on the intermediate transfer medium is secondarily transferred to the recording medium by making the secondary transfer roller abut on the intermediate transfer medium in the course of performing the image forming process for the black toner.